Clear glass composition with high visible transmittance

ABSTRACT

A high transmittance fairly clear/neutral colored glass composition is provided. An oxidizing agent(s) such as cerium oxide (e.g., CeO 2 ) or the like is added to the glass batch in order to realize very oxidized conditions (i.e., to significantly lower the redox of the resulting glass). As a result of the oxidizing agent(s) used in the batch, the iron is oxidized to a very low FeO (ferrous state) content. For example, this may result in a glass having a glass redox value of no greater than 0.12 (more preferably &lt;=0.10; even more preferably &lt;=0.08; and most preferably &lt;=0.05) and a % FeO (i.e., ferrous content) of from 0.0001 to 0.05%. In certain example embodiments, in order to compensate for yellow or yellow-green coloration a small amount of cobalt (Co) may be provided in the glass to enable it to realize a more neutral color.

PRIORITY CLAIM

This application is a continuation-in-part (CIP) of U.S. patentapplication Ser. Nos. 10/336,859, filed Jan. 6, 2003, and Ser. No.10/457,552, filed Jun. 10, 2003, which is a Divisional of Ser. No.10/056,051, filed Jan. 28, 2002 (now U.S. Pat. No. 6,610,622), theentire disclosures of which are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to glass compositions and methods of making thesame. More particularly, this invention relates to glass having highlight transmittance in the visible range and/or fairly neutral color.Such glass compositions are useful, for example, in architecturalwindows, patterned glass applications, residential windows, furniture,solar cells, and/or automotive windows.

Glass that is fairly neutral or clear in color, and highly transmissiveto visible light (e.g., at least 75% transmissive, or even morepreferably at least 80% transmissive), is sometimes desirable. One wayof achieving such a glass is to use very pure base glass materials(e.g., substantially free of colorants such as iron). However, basematerials with a high degree of purity are expensive and thus not alwaysdesirable and/or convenient. In other words, for example, the removal ofiron from glass raw materials has certain practical and/or economicallimits.

As can be appreciated from the above, glass raw materials (e.g., silica,soda ash, dolomite, and/or limestone) typically include certainimpurities such as iron. The total amount of iron present is expressedherein in terms of Fe₂O₃ in accordance with standard practice. However,typically, not all iron is in the from of Fe₂O₃. Instead, iron isusually present in both the ferrous state (Fe²⁺; expressed herein asFeO, even though all ferrous state iron in the glass may not be in theform of FeO) and the ferric state (Fe³⁺). Iron in the ferrous state(Fe²⁺; FeO) is a blue-green colorant, while iron in the ferric state(Fe³⁺) is a yellow-green colorant. The blue-green colorant of ferrousiron (Fe²⁺; FeO) is of particular concern when seeking to achieve afairly clear or neutral colored glass, since as a strong colorant itintroduces significant color into the glass. Ferrous iron is typically astronger colorant than ferric iron. Thus, while iron in the ferric state(Fe³⁺) is also a colorant, it is of less concern when seeking to achievea glass fairly clear in color.

In view of the above, it is apparent that there exists a need in the artfor a new glass composition which enables a glass to have fairly clearcolor and/or high visible transmission, without having to resort toextremely pure (i.e., free of iron) glass raw materials.

U.S. Pat. No. 6,218,323 discloses a neutral colored high transmissionglass which can achieve a visible transmission of at least 89%. In orderto achieve these characteristics, the glass of the '323 patent requiresa very low total iron (expressed herein as Fe₂O₃) content of 0.01 to0.03%, and a standard glass redox (FeO/Fe₂O₃) of 0.25 to 0.35. However,in some instances it is difficult (e.g., expensive and/or impractical)to achieve such a low total iron content of 0.01 to 0.03%. Thus, it willbe appreciated by those skilled in the art that there exists a need fora clear glass composition capable of achieving high visible transmissionand relatively neutral color regardless of whether or not the total ironis in the very low 0.01 to 0.03% range.

BRIEF SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION

It is an object of this invention to provide a glass capable ofachieving a high visible transmission (e.g., of at least about 85%, morepreferably of at least about 88%, and most preferably at least about90%).

It is another object of this invention to provide a glass capable ofachieving a high visible transmission when including a total ironcontent (expressed herein as Fe₂O₃) from 0.01 to 0.2%. In certainexample embodiments, the glass may have a total iron content of from0.01 to 0.15%, more preferably from 0.02 to 0.12%, and most preferablyfrom 0.04 to 0.10%.

In order to achieve a high visible transmission and/or fairly neutralcolor given such a total iron content, in certain example embodiments ofthis invention an oxidizing agent(s) such as cerium oxide (e.g., CeO₂)or the like is added to the glass batch in order to realize veryoxidized conditions (i.e., to significantly lower the redox of theresulting glass). As a result of the oxidizing agent(s) used in thebatch, the iron is oxidized to a very low FeO (ferrous state) content.This is advantageous since ferrous iron (Fe²⁺; FeO) is a much strongercolorant than is ferric iron (Fe³⁺). In certain example embodiments ofthis invention, the resulting glass has a glass redox value of nogreater than 0.12 (more preferably <=0.10; even more preferably <=0.08;and most preferably <=0.05) and an % FeO (i.e., ferrous content) of from0.0001 to 0.05% (more preferably from 0.0001 to 0.01%; most preferablyfrom 0.001 to 0.008%).

In certain example embodiments of this invention, even given theabove-listed ferrous content (% FeO) and low glass redox value, theglass may still realize a yellow or yellow-green coloration. In order tocompensate for such coloration, a small amount of cobalt (Co) may beprovided in the glass to enable it to realize a more neutral color incertain example embodiments of this invention. Thus, the use of theoxidizing agent(s) decolorizes in a chemical fashion, and thesimultaneous use of Co in certain example embodiments decolorizes in aphysical fashion.

Another object of certain example embodiments of this invention is tofulfill one or more of the above-listed objects.

In certain example embodiments of this invention, one or more of theabove-listed objects and/or needs is/are fulfilled by providing a glasscomprising: a base glass portion comprising: SiO₂ 67 to 75% Na₂O 10 to20% CaO  5 to 15% MgO 0 to 8% Al₂O₃ 0 to 5% K₂O 0 to 5   

a colorant portion comprising (or consisting essentially of): total iron(expressed Fe₂O₃):  0.01 to 0.20% cobalt oxide: 0.1 to 15 ppm chromiumoxide:   0 to 10 ppm titanium oxide:    0 to 0.5% glass redox: <=0.10 %FeO: 0.0001 to 0.05%and wherein the glass has a visible transmission of at least about 85%.

In certain other example embodiments of this invention, one or more ofthe above-listed objects is/are fulfilled by providing a glasscomprising: total iron (expressed Fe₂O₃):  0.01 to 0.15% cobalt oxide:0.1 to 15 ppm chromium oxide:   0 to 10 ppm titanium oxide:    0 to 0.5%glass redox: <=0.10 % FeO: 0.0001 to 0.05%wherein the glass has a visible transmission of at least about 85%.

In certain other example embodiments of this invention, one or more ofthe above-listed objects is/are fulfilled by providing a glasscomprising: total iron (expressed Fe₂O₃):  0.01 to 0.15% glass redox:<=0.12 % FeO: 0.0001 to 0.05%wherein the glass has a visible transmission of at least about 85%.

DETAILED DESCRIPTION OF CERTAIN EXAMPLE EMBODIMENTS OF THE INVENTION

Glass according to certain example embodiments of this invention iscapable of achieving high visible transmission while at the same timerealizing fairly neutral or clear color. Glasses according to differentembodiments of this invention may be used in the context(s) ofarchitectural windows, patterned glass applications, residentialwindows, furniture, solar cells, and/or automotive windows.

Certain glasses according to this invention utilize soda-lime-silicaflat glass as their base composition/glass. In addition to basecomposition/glass, a unique colorant portion is provided in order toachieve a glass that is fairly clear in color and/or has a high visibletransmission. An example soda-lime-silica base glass according tocertain embodiments of this invention, on a weight percentage basis,includes the following basic ingredients: TABLE 1 EXAMPLE BASE GLASSIngredient Wt. % SiO₂ 67-75% Na₂O 10-20% CaO  5-15% MgO 0-8% Al₂O₃ 0-5%K₂O 0-5%

Other minor ingredients, including various refining aids, such as SO₃,carbon, and the like may also be included in the base glass. In certainembodiments, for example, glass herein may be made from batch rawmaterials silica sand, soda ash, dolomite, limestone, with the use ofsalt cake (SO₃) and/or Epsom salts (e.g., about a 1:1 combination ofboth) as refining agents. For example, and without limitation, the glassmay include from 0-1% (by weight) SO₃ in certain example embodiments ofthis invention, more preferably from 0.1 to 0.3%, still more preferablyfrom 0.18 to 0.26%, with an example amount being 0.23%. Preferably,soda-lime-silica based glasses herein include by weight from about10-15% Na₂O and from about 6-12% CaO. While a soda-lime-silica baseglass set forth above is preferred in certain embodiments of thisinvention, this invention is not so limited. Thus, other base glasses(e.g., borosilicate glass) may instead be employed in alternativeembodiments of this invention.

In addition to the base glass (e.g., see Table 1 above), in making glassaccording to the instant invention the glass batch includes materials(including colorants and/or oxidizers) which cause the resulting glassto be fairly neutral in color and/or have a high visible lighttransmission. These materials may either be present in the raw materials(e.g., small amounts of iron), or may be added to the base glassmaterials in the batch (e.g., cerium, cobalt, etc.). In certainpreferred embodiments, the resulting glass has visible transmission ofat least 85%, more preferably at least 88%, and most preferably at least90% (e.g., at a reference thickness of about 0.219 inches or 5.56 mm).

In certain embodiments of this invention, in addition to the base glass,the glass batch and/or final glass includes materials as set forth inTable 2 below (in terms of weight percentage of the total glasscomposition, unless otherwise listed as ppm in the case of cobalt):TABLE 2 EXAMPLE COLORANTS AND OXIDIZER CERIUM Ingredient GeneralPreferred More Preferred Best total iron (Fe₂O₃): 0.01-0.20% 0.01-0.15%0.02-0.12% 0.04 to 0.10% cobalt oxide: 0.1 to 15 ppm 0.3 to 10 ppm 0.5to 5 ppm 0.5 to 3 ppm cerium oxide: 0.005-1.0% 0.01-1.0% 0.01-0.5% 0.05to 0.2% titanium oxide: 0 to 0.5% 0 to 0.2% 0.001 to 0.05% 0.01 to 0.02%chromium oxide: 0 to 10 ppm 0 to 8 ppm 0 to 5 ppm 1 to 5 ppm glassredox: <=0.12 <=0.10 <=0.08 <=0.05 % FeO: 0.0001-0.05% 0.0001-0.01%0.001-0.008% 0.001-0.003%

It can be seen from the table above that small or trace amounts oftitanium oxide (e.g., TiO₂ or other stoichiometry) and/or chromium oxidemay be present in certain example instances (such amounts of titania orchromium oxide, typically referred to as colorants, may be intentionallyor unintentionally provided in the resulting glass in differentembodiments of this invention). It is also possible to eliminate cobaltin certain example embodiments of this invention. It should beappreciated that small amounts of other materials (e.g., refining aids,melting aids, and/or impurities) may be present (intentionally orunintentionally) in the glass such as manganese, molybdenum, tin,carbon, chlorine, zinc, zirconium, Si, sulfate, fluorine, lithium and/orstrontium, without taking away from the purpose(s) and/or goal(s) of theinstant invention.

It is noted that due to the small amounts of cerium oxide used, thatmaterial is not referred to as a colorant herein (instead, it acts as anoxidizer). Cerium, for example, may be added to the batch in the form ofCeO₂, and may take the form of Ce₂O₃ (or any other suitable form) in thefinal glass. According to certain example embodiments of this invention,the presence of cerium oxide (e.g., CeO₂) as an oxidizer in the glassbatch acts as a chemical decolorizer since during melting of the glassbatch it causes iron in the ferrous state (Fe²⁺; FeO) to oxidize to theferric state (Fe³⁺) as illustrated by the following equation:Fe²⁺+Ce⁴⁺=Fe³⁺+Ce³⁺  (1)

Equation (1) shows that the presence of cerium oxide in the glass batchcauses an amount of the strong blue-green colorant of ferrous iron(Fe²⁺; FeO) to oxidize into the weaker yellow-green ferric iron colorant(Fe³⁺) during the glass melt (note: some ferrous state iron will usuallyremain in the resulting glass, as potentially may some Ce⁴⁺).Accordingly, a significant portion of the CeO₂ added to the originalglass batch prior to the melt is transformed during the melt into Ce₂O₃which is present in the resulting glass. The aforesaid oxidation of theiron tends to reduce coloration of the glass, and does not significantlydecrease visible light transmission of the resulting glass (in certaininstances, this may even causes visible transmission to increase).

In order to achieve the combination of high visible transmission andfairly neutral or clear color, in certain example embodiments of thisinvention an oxidizing agent(s) such as cerium oxide (e.g., CeO₂) or thelike is added to the glass batch in order to realize very oxidizedconditions (i.e., to significantly lower the redox of the resultingglass). Other oxidizing agent(s) such as sulfates and/or crystallinewater may be used together with or instead of cerium oxide in certainexample embodiments of this invention. As a result of the oxidizingagent(s) used in the batch, the iron is oxidized to a very low FeO(ferrous state) content. This is advantageous since ferrous iron (Fe²⁺;FeO) is a much stronger colorant than is ferric iron (Fe³⁺). Theoxidizing agent(s) enables a resulting glass having a glass redox valueof no greater than 0.12 (more preferably <=0.10; even more preferably<=0.08; and most preferably <=0.05) and a % FeO content (i.e., ferrouscontent) of from 0.0001 to 0.05% (more preferably from 0.0001 to 0.01%;most preferably from 0.001 to 0.008%). The batch redox (as opposed tothe glass redox) is typically from about +2 to +20 in different exampleembodiments of this invention, more preferably from about +5 to +15.

In certain example embodiments of this invention, even given theabove-listed ferrous content (% FeO) and low glass redox value, theglass may still realize a yellow or yellow-green coloration. In order tocompensate for such coloration, a small amount of cobalt (Co) may beprovided in the glass to enable the glass to realize a more neutralcolor in certain example embodiments of this invention. Thus, the use ofthe oxidizing agent(s) decolorizes (i.e., moves color more towardneutral) in a chemical fashion, and the simultaneous use of Co incertain example embodiments decolorizes in a physical fashion. Thisrepresents a significant advantage in the art, as high visibletransmission and fairly neutral color may be achieved regardless ofwhether or not the total iron is in the very low range of 0.01 to 0.03%.

The total amount of iron present in the glass and in the colorantportion thereof is expressed herein in terms of Fe₂O₃ in accordance withstandard practice. This, however, does not imply that all iron isactually in the form of Fe₂O₃. Likewise, the amount of iron in theferrous state is reported herein as FeO, even though all ferrous stateiron in the glass may not be in the form of FeO. The proportion of thetotal iron in the ferrous state (i.e., FeO) is used to determine theredox state of the glass (i.e., glass redox). Herein, glass redox isexpressed as the ratio FeO/Fe₂O₃, which is the weight percentage (%) ofiron in the ferrous state (expressed as FeO) divided by the weightpercentage (%) of total iron (expressed as Fe₂O₃). Thus, Fe₂O₃ hereinmeans total iron and FeO means iron in the ferrous state. Iron in theferrous state (Fe 2; FeO) is a blue-green colorant, while iron in theferric state (Fe³⁺) is a yellow-green colorant. According to certainembodiments of this invention, the colorant portion of the glasscomposition herein is characterized by a redox value (i.e., FeO/Fe₂O₃)of no greater than 0.12 (more preferably no greater than 0.10, even morepreferably no greater than 0.08 and most preferably no greater than0.05, and sometimes no greater than 0.03) as listed above in Table 2.

Cobalt (Co) is a blue colorant, largely present in glass as Co²⁺ ions.However, other oxide states of Co are also possible in glasses accordingto this invention. It is conventional to add cobalt colorant as CO₃O₄and report its content in this form; even though this may not describethe state of oxidation of Co in the glass. Thus, unless expressly statedto the contrary, the terms cobalt oxide, CoO and CO₃O₄ as used hereineach include not only cobalt in this/these particular oxide state(s),but also include(s) cobalt which may be present in other oxide ornon-oxide state(s). Likewise, the terms cerium oxide, CeO₂ and Ce₂O₃ asused herein each include any form of cerium that may be present in theglass (or batch).

In certain example embodiments of this invention, an example colorantportion that is added to the base glass is substantially free ofchromium (Cr), nickel (Ni), erbium (Er), and/or selenium (Se). In anexample embodiment, the glass includes no more than about 0.005% (wt. %)Cr, more preferably no more than about 0.001% Cr, and even morepreferably no more than about 0.0001% Cr. In an example embodiment, theglass includes no more than about 0.001% Se, more preferably no morethan about 0.0001% Se. In an example embodiment, the glass includes nomore than about 0.005% (wt. %) Ni, more preferably no more than about0.001% Ni, and even more preferably no more than about 0.0001% Ni. In anexample embodiment, the glass includes no more than about 0.01% Er, morepreferably no more than about 0.001% Er, more preferably no more thanabout 0.0001% Er. It is noted that the term Cr includes oxides of Cr,and the terms Se, Er and Ni include respective oxides of these elements.While the glass is substantially free of Cr, Er, Ni and/or Se in certainexample embodiments of this invention, the invention is not so limitedunless specifically claimed.

In certain example embodiments of this invention, slag may be removedfrom batch and carbon used for refining purposes while furtherincreasing cerium in the batch in order to bring FeO levels to a rangeof from 0.0005 to 0.00015%. Removal of slag may be used to lower ferrouscontent. Thus, in certain example non-limiting embodiments of thisinvention the batch may be substantially slag-free (or have reduced slagamounts) in order to improve quality/color/higher transmittance.

It is noted that glasses according to this invention may be made via theknown float process in which a tin bath is utilized. It will thus beappreciated by those skilled in the art that as a result of forming theglass on molten tin in certain exemplary embodiments, small amounts oftin or tin oxide may migrate into surface areas of the glass on the sidethat was in contact with the tin bath during manufacture (i.e.,typically, float glass may have a tin oxide concentration of 0.05% ormore (wt.) in the first few microns below the surface that was incontact with the tin bath). Interaction between the glass and tin canaffect the optical properties of a very thin layer just inside the glassin certain instances.

Glasses of this invention, as stated above, may in certain examplenon-limiting embodiments achieve the following color/solarcharacteristics characterized by high visible transmission and fairlyneutral or clear coloration. In certain embodiments, glasses hereininclude one or more of the following color/solar characteristics whenmeasured at an example non-limiting reference thickness of about 0.219inches: TABLE 3 Example Transmissive Color/Solar CharacteristicsCharacteristic General More Preferred Best Lta (visibletransmittance): >=85% >=88% >=90% UV_(transmission) (% UV): <=80% <=75%<=72% L* (Il1. D65, 10 deg. 85-99 90-99 94-98 observer): a* (Il1. D65,10 deg. −1.5 to +1.5 −1 to +1 −0.5 to +0.5 observer): b* (Il1. D65, 10deg. −1.5 to +1.5 −1 to +1 −0.5 to +0.5 observer): Y(Ltc): 85-95 88-9289-91 x 0.2 to 0.4 0.25 to 0.35 0.30 to 0.32 y 0.2 to 0.4 0.25 to 0.350.30 to 0.32

Glasses of certain embodiments of this invention achieve the aboveunique characteristics (i.e., high visible transmission, high Ltc,and/or fairly neutral or clear color) through the use of the uniquecolorant portions and low glass redox values discussed herein. The lowredox and unique colorant portions discussed herein enable the glass toachieve this combination without the need for significant amounts of Cr,Se, Ni, and/or Er.

EXAMPLES

The glasses of this invention may be made from batch ingredients usingwell known glass melting and refining techniques. For example, in aconventional batch technique for melting, the following base glass batchwas used for the Examples herein (note: the below-listed ingredients inthe batch will add up to 100% by weight once oxides thereof areaccounted for; thus, they need not add up to one hundred as rawmaterials—fusion factor of 0.83). TABLE 4 Base Glass for Examples BatchIngredient for Base Glass Parts by Wt. sand 71.5 soda ash 23.7 dolomite18.32 limestone 6.1

For Examples 1-6, an experimental 100 g glass melt was made in aplatinum crucible using a standard electric melting furnace set-up forsoda-lime-silica composition. The melting temperature was about 1500degrees C., the melting time was about 4 hours, the annealingtemperature was about 620-680 degrees C., and an annealing time of about0.5 hrs. was used for allowing cooling to room temperature by inertiaafter the annealing furnace is shut down. The glass was cast intographite molds, annealed and cooled down, then ground and polished forvisual inspection and spectral measurements. Colorants, oxidizers andother refining agent(s) (e.g., cobalt, cerium oxide, crystalline waterand/or salt cake) were added to the aforesaid base glass in certainexamples herein. Table 5 below sets for the colorants (and cerium fromthe use of cerium oxide as an oxidizer) present in the final glasses(wt. % of total glass) according to the Examples 1-6 herein, as well ascertain solar/color/redox characteristics regarding the same. Lta, a*,b*, and L* were transmissive, and a*, b* and L* data were taken via Ill.D65, 10 deg. observer. Reducer(s) such as C, Si, SiO, sucrose and/orcalumite were used in amounts in order to achieve batch redoxes of from+5 to +15 in different examples. The elements are listed below in termsof wt. % of the final glass (except for cobalt oxide which is listed interms of ppm). The total iron was within the range of about 0.04 to 0.10(wt. %) for all examples, and the precise make-up of the iron can bedetermined from the below-listed glass redox values and the listed % FeOvalues. TABLE 5 Examples 1-6: colorants/solar properties/redoxElement/Property Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 total iron (Fe₂O₃):0.04 to 0.10 (for all examples) cobalt oxide (e.g., Co₃O₄): 1 ppm 2 ppm2 ppm 0.5 ppm 0 ppm 1 ppm cerium oxide: 0.1 0.075 0.06 0.07 0.06 0.09epsom refiner used? yes no no yes no yes glass redox (FeO/Fe₂O₃): 0.020.04 0.06 0.03 0.03 0.02 % FeO (spectral): 0.0013 0.0022 0.003 0.00180.0027 0.0015 Lta (vis. transmission %): 90.5 90.0 90.1 90.2 90.7 90.1(% UV): 69.2 70.5 72.5 70.8 70.8 69.5 L* (D65, 10 deg.): 96.7 95.9 95.995.9 96.3 95.9 a* (D65, 10 deg.): −0.23 −0.3 −0.3 −0.3 −0.4 −0.3 b*(D65, 10 deg): +0.44 +0.02 −0.02 +0.3 +0.9 +0.6 Y (Ltc): 90.5 90.1 90.190.3 90.7 90.1 x 0.3105 0.3096 0.3095 0.3102 0.3111 0.3107 y 0.31720.3164 0.3164 0.3172 0.3183 0.3177

Another Example 7 according to an example embodiment of this inventionis set forth below, with the amounts of the various elements beinglisted in terms of weight percentage as measured in the final glass(glass was about 5.6 mm thick as an example reference thickness). TABLE6 Example 7: colorants/solar properties/redox Element/Property Ex. 7SiO₂: 72.78% Na₂O: 13.55% CaO:  8.43% MgO:  4.21% Al₂O₃:  0.16% K₂O:0.055% total iron (Fe2O3): 0.052% cobalt oxide (e.g., Co3O4): 1-2 ppm(≈0.0001 to 0.0002%) cerium oxide: 0.14 to 0.15% glass redox(FeO/Fe2O3):  0.02 % FeO (spectral): 0.0013%  salt cake (SO3): 0.229%TiO₂: 0.016% Cr₂O₃: 3 ppm Lta (vis. transmission %): 90-91%

It is noted that luminous transmittance (Lta) (2 degree observer) isunderstood in the art, and is used herein in accordance with its knownmeaning. This term is also known as Ill. A visible transmittance(380-780 nanometers inclusive), and its measurements are made inaccordance with CIE Publication 15.2 (1986) and ASTM E308. The terms,and characteristics, of ultraviolet light transmittance (% UV) infraredenergy transmittance (% IR), dominant wavelength (λ), total solar energytransmittance (% TS), and excitation purity (i.e. % “purity”, or Pe) arealso well understood terms in the art, as are their measurementtechniques. Such terms are used herein, in accordance with their wellknown meaning, e.g., see U.S. Pat. No. 5,308,805. In particular,ultraviolet transmittance (% UV) is measured herein using Parry Moon AirMass=2 (300-400 nm inclusive, integrated using Simpson's Rule at 10 nmintervals). IR transmittance is conventionally measured using Simpson'sRule and Parry Moon Air Mass=2 over the wavelength range 800-2100 nminclusive at 50 nm intervals. Dominant wavelength (DW) is calculated andmeasured conventionally in accord with the aforesaid CIE Publication15.2 (1986) and ASTM: E 308-90. The term “dominant wavelength” includesboth the actual measured wavelength and, where applicable, itscalculated complement. Excitation purity (Pe or % “purity”) is measuredconventionally in accordance with CIE Publication 15.2 (1986) and ASTM:E 308-90.

The glass redox is defined above. However, batch redox is different fromglass redox. Batch redox is known in the art as being generally based onthe following. Each component of the batch is assigned a redox number,and the batch redox is calculated as the sum total of the same. Thecalculations are based on the amount of a component per 2,000 kg ofsand. The batch redox number is calculated before the glass is made(i.e., from the batch). A detailed discussed of how “batch redox” isdetermined is provided in The redox number concept and its use by theglass technologist, W. Simpson and D. D. Myers (1977 or 1978), theentire disclosure of which is hereby incorporated herein by reference.In contrast, as explained above, the glass redox is calculated after theglass has been made from spectral data, and is a ratio of % FeO (e.g.,from a spectrum) to total iron in the glass (e.g., from chemicalanalysis).

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1-27. (canceled)
 28. A glass comprising: total iron (expressed Fe₂O₃): 0.01 to 0.20% cobalt oxide: 0.1 to 15 ppm glass redox: <=0.12 ceriumoxide: 0.005 to 1.0%

wherein the glass has a visible transmission of at least about 85%. 29.The glass of claim 28, wherein the glass is colored as follows: a* −1 to+1 b* −1 to +1.


30. The glass of claim 28, wherein the glass is colored as follows: a*−0.5 to +0.5 b*  −0.5 to +0.5.


31. The glass of claim 28, comprising: total iron (expressed Fe₂O₃):0.01 to 0.15% cobalt oxide: 0.3 to 10 ppm glass redox: <=0.08 % FeO:0.0001 to 0.05%.


32. The glass of claim 28, further comprising from 0 to 10 ppm chromiumoxide, and from 0 to 0.2% titanium oxide.
 33. The glass of claim 28,wherein the glass has a visible transmission of at least 88%.
 34. Theglass of claim 28, wherein the glass has a visible transmission of atleast 90%, and a UV % transmission of no greater than about 75%. 35-39.(canceled)